Ophiura sarsii

Ophiura sarsii, commonly called the notched brittle star, is a cold-water, bottom-dwelling marine species that lives in the Arctic and Sub-Arctic seas. It was first described by Christian Frederik Lütken in 1855. These brittle stars are typically red or brown, grow to a large size, and are very numerous in their habitats. They can survive for as long as 27 years.

Adults have arms that reach up to 90 millimeters in length, which is about three to four times the diameter of the central disk. The disk itself is usually up to 25 millimeters across, though it can be as wide as 40 millimeters. It is rigid and heavily calcified—much larger than the disk of Ophiocten sericeum, a similar cold-water brittle star that shares the same environment and maxes out at 18 millimeters.

As O. sarsii leaves its larval stage, the disk becomes pentagonal with small holes. Over time, it develops spines, arms, arm joints, and protective plates. This brittle star can live up to 27 years. Studies show it goes through an eight-year period of fast growth, followed by four to five years with no growth, and then another fast-growth phase until death.

Habitat

Growth is measured using bands on the disk. Habitat O. sarsii is found in the northern Atlantic and Pacific Oceans, as well as throughout the Arctic Ocean. It lives mainly in the bathyal zone of the open ocean, sometimes covering up to 96% of the seabed. In the Arctic, it prefers slopes and shelves with soft bottoms.

Prey

It outnumbers all other brittle star species in its habitat, making up 71% of the benthic and epibenthic brittle stars in the Arctic Ocean. Diet and feeding habits Prey: Though mostly carnivorous, O. sarsii is a trophic generalist. Its primary food is amphipods, but it also eats arthropods, molluscs, cnidarians, and annelids.

Predators

Its diet is heavily focused on the amphipod families Ampeliscidae and Lysianassidae, which made up 54–70% of stomach contents in a study by Harris et al. (2009). Predators: Benthic carnivorous fish and crabs prey on O. sarsii. It is the main food of the American plaice in the Gulf of Maine; one study by Packer et al. (1994) found that 82% of plaice gut contents were ophiuroids, with 65% of those being O. sarsii. More than half of adult red king crabs also eat brittle stars like this one.